The present invention relates to polypeptides and polynucleotides expressing the human Sef b-d isoforms (hSefb-d), and more particularly, to the use of such isoforms in the inhibition of uncontrolled malignant proliferation of solid tumors.
Solid tumors account for the majority of human tumors and among them, carcinomas of an epithelial origin, account for over 80%. Conventional therapies for solid tumors involves the administration of anti-tumor drugs such as thymidylate synthase inhibitors (e.g., 5-fluorouracil; Rose M G et al., 2002; Clin Colorectal Cancer. 1: 220-9), nucleoside analogs [e.g., gemcitabine (Gemzar); Seidman A D., 2001. Oncology (Huntingt). 15: 11-14), non-steroidal (e.g., anastrozole and letrozole) and steroidal (exemestane) aromatase inhibitors (Lake D E and Hudis C., 2002; Cancer Control; 9: 490-8), taxanes and topoisomerase-I inhibitors (e.g., irinotecan; Van Cutsem, E. 2004; The Oncologist, 9, Suppl 2, 9-15). However, the use of such drugs often fails due to the development of drug resistance by the cancer cells. Thus, despite the tremendous progress in understanding tumor biology and early detection of cancer, cancer mortality rates have not been significantly reduced.
The growth of solid tumors depends on nutrients and oxygen which are supplied by the tumor vasculature. The growth of new blood vessels into the tumor is controlled by paracrine signals, many of which are mediated by protein ligands which modulate the activity of transmembrane tyrosine kinase receptors (RTK). These include vascular endothelial growth factor (VEGF) and its receptor families (VEGFR-1, VEGFR-2, neuropilin-1 and neuropilin-2), Angiopoietins 1-4 (Ang-1, Ang-2) and their respective receptors (Tie-1 and Tie-2), basic fibroblast growth factor (bFGF), platelet derived growth factor (PDGF), transforming growth factor β (TGF-β) and their receptors. Thus, it was conceivable that inhibition of angiogenesis can inhibit the growth of solid tumors.
Indeed, several studies have demonstrated that anti-angiogenic agents such as Endostatin, AGM-1470, angiostatin, BB-94, 2-Methoxyestradiol (2-ME) and Taxol in can inhibit tumor growth in vivo (Boehm et al., 1997; Nature; 390: 404-7; Bergers et al., 1999; Science; 284: 808-12; Klauber N et al. 1997; 57: 81-6). However, the mechanisms by which such agents exert their anti-tumor effect remain unclear (O′Reilly et al., 1997; Oreilly et al., 1996).
The interest in FGFs and their receptors as potential drug targets arose from their wide distribution in cells of different lineages and their mitogenic and angiogenic activities, two essential activities for solid tumor growth and metastasis (Zetter, B. R. 1998; Annu. Rev. Med. 49: 407-424). The oncogenic potential of FGFs is well documented in both, in-vitro studies and animal model systems (McKeehan, W. L., et al., 1998; Prog. Nucleic. Acid. Res. Mol. Biol. 59: 135-176; Szebenyi, G. and Fallon, J. F. 1999; Int. Rev. Cytol. 185: 45-106; Shaoul, E., et al., 1995; Oncogene 10: 1553-1561; Miki, T., et al., 1991; Science 251: 72-75; Kitsberg, D. I. and Leder, P. 1996. Oncogene 13: 2507-2515). Moreover, a variety of human carcinomas including pancreatic, endometrial and prostate carcinomas, overexpress FGFs (FGF-1, FGF-2 and FGF-7) and their receptors (KGFR and FGFR1), and tumor aggressiveness is correlated with the level of expression of these receptors (Giri, D., et al., 1999; Clin. Cancer Res. 5: 1063-1071; Visco, V., et al., 1999; Int. J. Oncol. 15: 431-435; Siegfried, S., et al., 1997; Cancer 79: 1166-1171; Ishiwata, T., et al., 1998; Am. J. Pathol. 153: 213-222; Kornmann, M., et al., 1998; Pancreas 17: 169-175; Siddiqi, I., et al., 1995; Biochem. Biophys. Res. Commun. 215: 309-315). Altogether, these observations strongly suggest the involvement of FGFs and their receptors in the malignant process. Thus, developing tools to target FGFRs, and their signaling pathways could be very useful for cancer therapy.
Several mechanisms collectively known as “negative signaling” have been evolved to attenuate signaling by RTKs (Christofori, G., 2003). One such mechanism involves ligand-induced antagonists of RTK signaling. The Sprouty and SPRED (Sprouty related EVH1-domain-containing) proteins belong to this category, and are regarded as general inhibitors of RTK signaling. They suppress the RTK-induced mitogen-activated protein kinase (MAPK) pathway (reviewed in Christofori, G., 2003; Dikic and Giordano, 2003).
Sef (for Similar Expression to FGF genes) is a newly identified antagonist of fibroblast growth factor (FGF) signaling. Sef encodes a putative type I transmembrane protein that is conserved across zebrafish, mouse and human but not in invertebrates (Furthauer, M., et al., 2002; Tsang M., et al., 2002; Lin, W., et al., 2002). Zebrafish Sef (zfSef) antagonizes FGF activity during embryogenesis by acting as a feedback-induced antagonist of the Ras/MAPK mediated FGF-signaling (Furthauer, M., et al., 2002; Tsang M., et al., 2002). Subsequent studies showed that the mouse (Kovalenko D, 2003) homologue of zfSef similarly inhibit FGF-induced activation of MAPK, and FGF-induced activation of protein-kinase B (pkB/Akt), a key protein in the phosphatidylinositol-3 (PI3) kinase pathway. On the other hand, the mSef was unable to inhibit PDGF-, EGF- or calf serum-induced phosphorylation of ERK in NIH 3T3 cells (Kovalenko D, 2003). Other studies showed that the human Sef homologue (which is later referred to as hSef-a by the present inventor) is capable of inhibiting FGF- and NGF-induced differentiation of PC12 cells (Xiong et al., 2003; JBC 278: 50273-50282).
The expression level of human Sef in normal and malignant tissues has been controversial. While Yang R B., et al (J. Biol. Chem. 2003, 278:33232-8) found that Sef is expressed a variety of breast cancer tissues, Darby S, (Oncogene. 2006, 25: 4122-7) found that loss of Sef expression is associated with high grade and metastais of prostate cancer only. Thus, to date, cancer diagnosis which is based on Sef expression level has not been suggested. In addition, none of these studies have suggested using Sef expression for staging of cancer, determining disease course and/or cancer prognosis and/or for selecting an anti-cancer therapy regimen.
There is thus, a widely recognized need to develop agents suitable for diagnosing and treating cancerous solid tumors.